A steering apparatus for a vehicle has been known in which the relationship between changes in the steering angle due to steering operation and changes in the steered angle of steerable wheels is non-linear (for example, Patent Document 1). The steering apparatus includes a first shaft and a second shaft, which are coupled to each other via a joint mechanism so as to be eccentric relative to each other. The first shaft is coupled to a steering wheel, and the second shaft is coupled to steerable wheels via a rack and pinion mechanism. Rotation of the first shaft caused by steering operation is non-linearly transmitted to the second shaft by the joint mechanism.
Specifically, as shown in FIG. 7, a steering apparatus 21 includes a first shaft 23 coupled to a steering wheel 22, a joint mechanism 25, and a second shaft 24 coupled to the first shaft 23 via the joint mechanism 25. A cam 27 having a cam groove 26 is provided at one end of the first shaft 23. The cam groove 26 extends in a direction perpendicular to the first shaft 23. The cam groove 26 receives a cam follower 28 that slides within the cam groove 26. A coupling portion 29 is formed at one end of the second shaft 24 that is coupled to a rack and pinion mechanism (not shown). The coupling portion 29 has an eccentric pin 30 located at a position eccentric relative to the second shaft 24. The eccentric pin 30 extends along the axial direction of the second shaft 24. The joint mechanism 25 is formed by the eccentric pin 30 and the cam follower 28, which are connected to each other. The first shaft 23 and the second shaft 24 are coupled to each other at an eccentric position by the joint mechanism 25, so that rotation of the first shaft 23 is transmitted to the second shaft 24 through the joint mechanism 25.
That is, rotation of the cam 27 on the first shaft 23 is permitted by sliding motion of the cam follower 28 in the cam groove 26 and rotation of the cam follower 28 about the eccentric pin 30. As shown in FIG. 8, the eccentric pin 30, which is coupled to the cam follower 28, moves along a circle concentric with the second shaft 24 as the cam 27 rotates and the cam follower 28 slides. Accordingly, rotation of the first shaft 23 is transmitted to the second shaft 24.
A circle shown by a broken line in FIG. 8 indicates the path of the axis of the eccentric pin 30, which moves as the cam 27 rotates. Circles formed by lines having a long dash alternating with two short dashes represent positions of the eccentric pin 30 (P0, P1, P2, P1′, P2′, P3) corresponding to the rotation angle (every 60°) of the cam 27. As shown in FIG. 8, the closer to the position P0 the eccentric pin 30, the greater the change in the position of the eccentric pin 30 relative to a change in the rotation angle of the cam 27. Also, the closer to the position P3 the eccentric pin 30, the smaller a change in the position of the eccentric pin 30 relative to a change in the rotation angle of the cam 27.
According to this configuration, a non-linear relationship is established between changes in rotation angle of the first shaft 23 caused by steering operation and changes in rotation angle of the second shaft 24, which defines the amount of change in steered angle of the steerable angle. For example, when the eccentric pin 30 is at the position P3, this position is set as a neutral steering position (steering angle is zero). Also, when the eccentric pin 30 is at the position P0, the position is set as the maximum steered angle. Thus, in a range where the steering angle is small, a change in the steered angle corresponding to a change in the steering angle is small. On the other hand, in a range where the steering angle is great, a change in the steered angle corresponding to a change in the steering angle is great. Accordingly, it is possible to improve driving stability when traveling straight forward and the turning performance in ranges of large steering angles, using a simple structure.